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A cloud chamber is a simple device that allows you to observe the decay of radioactive materials. Here’s how to make your own…


  • mightyohm

    Don’t they mean Polonium? :-)

    • Wobbles

      yes that is what i think. i tried writing “penolium” but nope.

  • austin y.

    My grandfather showed me this when i was real young. We used an alcohol soaked black cloth over the dry ice, which was sitting in the lid of a jar, with the jar upside down, covering the cloth. At the right angle with the flashlight, you could see what looked like snow slowly falling from the top of the jar. We didn’t have a radiation source, but this alcohol “snow” would create little explosions when hit by a cosmic particle.

  • justDIY

    The cloud chamber science girl and the weird guy made a few months back worked out better, plus it didn’t need a huge slab of dry ice. At the nearby Meijer megamart, only a one hour round trip drive, it costs $20/lb for the cold stuff.

    I’m curious, does it need to be synthetic alcohol because the radiation likes it better, or could grain alcohol be used too?

    • oskay

      >I’m curious, does it need to be synthetic alcohol because the radiation likes it better, or could grain alcohol be used too?

      The important thing is that it’s relatively pure alcohol, and it’s not so hard to obtain isopropanol in relatively pure form. Pure ethanol will work, but easily-obtained food-grade ethanol is usually diluted too much.

      75% Everclear will not work, for example. I have not come across the 95% Everclear, but from what I’ve heard it’s so-so as a cloud chamber medium. “Pure” denatured alcohol should be a good choice.

  • Jim

    You can get a small amount of Americium from a smoke detector for a radiation source. (I think)

    I had a book that showed how to connect an external electric field to the chamber to make the particles move around the field.

    Cool Stuff

  • Apis

    I love cloud chambers. You can actually see individual particles (or their trails at least)! :) This is a low tech version of the LHC detector. You can distinguish charged particles with an electric field, or easier perhaps, with a magnet. Charged particle beta decay (electrons or positrons (antimatter!)) will be affected by the field and will not have a straight path (unlike the alfa-particles). If done a certain way, their paths will be spirals. The direction it turns depends on if it’s an electron (negative charge) or positron (positive charge), and the direction of the magnetic/electric field you apply (see Lorenz force on wikipedia or hyperphysics: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfor.html#c2 ). :D

    • Dave Bell

      “Charged particle beta decay (electrons or positrons (antimatter!)) will be affected by the field and will not have a straight path (unlike the alfa-particles).”

      Alpha particles are also charged (+2), but are far more massive (x7300), so it’s correspondingly harder to make their tracks curve measurably.

  • munch

    Where do I get the radiation at the end of a needle bit? I looked at the spectrum site, but as you didnt say what it was called, I have no idea what to look for.

    • Patrick Polowsky

      You can actually disassemble a smoke detector and use that.  

      • munch

        there is a bit of radioactive lead in a smoke detector?

        • http://web.ics.purdue.edu/~ppolowsk Patrick Polowsky

          It’s not lead, it’s usually Americium. But yes, smoke detectors use the radiation source to ionize the air.